Try this suggested option:
Explanation:
f(x)=2(2x²+4x)+3; ⇔
f(x)=4(x²+2x)+3; ⇔
f(x)=4(x²+2x+1)+3-4; ⇔
f(x)=4(x+1)²-1; ⇔
f(x)=(2x+1)(2x+3).
Then the roots are:
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